Aleksandrowicz was of Jewish descent, and after German invasion of Poland (during which he fought in the 72nd Infantry Regiment), he was imprisoned in the Kraków Ghetto (he managed to bury his research data beforehand and recover them after the war). He founded one of the three ghetto hospitals.[3][4] While in the ghetto, he was aided by one of the Polish Righteous, Józef Adamowicz (who was eventually caught and beaten to death by Nazi guards at the ghetto). Later, in 1943, Aleksandrowicz managed to escape the ghetto and became a physician of the Polish resistance, Armia Krajowa in the Kielce-Radom Independent Jodła Region, under a nom-de-guerreDoktor Twardy. Eventually he became a platoon leader. For his participation in the resistance, he received the Silver Cross of the Virtuti Militari.[4][5]